(1) Field of the Invention
The invention relates to a pressure-worked automatic control system with a closed loop, and, more specially, a position automatic control system for controllers, such as automatic control valves or the like, air-powered by a servo-motor, in the case of which the position of the servo-element is dependent on a spring placed between the servo-element or servo-motor and the sensing unit of the position automatic control system. Such position automatic control systems are more importantly used for overcoming disturbances, such as friction, changing levels of forces on the valve cone and the like, acting on the servo-element as far as possible. In the case of an automatic control valve with the help of a sensing unit of the position automatic control system a force (or a motion) produced by an actuating pressure is to undergo comparison with a force (or a motion), which, as far as poossible, is representative of the position of the valve driving rod. The force, changing dependently on the valve position, is normally produced by a spring changed in form springingly to a greater or lesser degree by the valve driving rod or any other servo element. The force representative of the actuating pressure is produced between this pressure takes effect on a diaphragm, a Bourdon tube, a piston or the like. If the two representative forces are not in balance an air-power operating system made up, for example of a mouthpiece and a power amplifier, whose input is joined with a plate moved by air from the mouthpiece, has such as effect that the pressure in the servo-motor of the air-power servo-element is changed till the valve driving rod has gone into that position which is representative of the actuating pressure, this being the purpose of the system.
(2) The condition of the art so far.
In past systems a normal screw or helical spring is used as a part representative of the valve position. Furthermore, in place of such a spring, use has been made of torsion rods. The two forms have their shortcomings, as will now be made clear. More specially, past designs take up much space because of their design, this being of little help in making a design of the system in which may be used widely, for example, in industry. The present invention has, more specially, the purpose of decreasing the amount of space needed by such an automatic control system. Further purposes are that of making a simpler design and making the system better with respect to operation and the chances of making adjustments.